Some human brains are nearly twice the size of others -- but how might that matter? Researcher have discovered that these differences in size are related to the brain's shape and the way it is organized. The bigger the brain, the more its additional area is accounted for by growth in thinking areas of the cortex, or outer mantle -- at the expense of relatively slower growth in lower emotional, sensory, and motor areas.

Source: Bigger human brain prioritizes thinking hub -- at a cost